Abstract/Summary

We combine the Olex echosounder dataset and high resolution NEXTMap digital surface models with aerial photographs and field observations to build on existing models of Late Devensian ice-sheet deglaciation in the Moray Firth area of northern Scotland. Morphological mapping of the offshore area, coupled with onshore sedimentological investigations suggest that following separation of British and Fennoscandian ice, the dynamics of the north-east sector of the British Ice Sheet was dominated by the Moray Firth ice stream. Onshore, a strongly convergent pattern of highly elongate, mega-scale rock drumlins, glacial grooves and till ridges documents ice flow at that time. Offshore, well-preserved, west-east trending tunnel valley networks indicate a period of significant subglacial drainage. A coherent suite of arcuate ridges preserved on the sea bed in the outer Moray Firth provide evidence for a major glacial advance, which probably took place c. 18 – 22 ka BP. Onshore, geomorphological, lithostratigraphical and sedimentological investigations indicate that at least two significant oscillations of the ice margin took place during retreat, leaving recessional moraines at Elgin and Ardersier. Between these two positions, suites of well-preserved De Geer moraines at Tarbat Ness suggest that relative sea level at the grounding line stood at least 55 metres above present OD. Towards the ice divide around Loch Shin, several fields of Rogen moraine may reflect a local change in thermal regime from cold-based to warm-based conditions, possibly associated with continued late-stage ice stream activity in NE Scotland.